I am not aware of any polarity requirement for the di-electric withstand test - factory or type, in 60950-1. But I have done some interesting experiments to duplicate effects discussed in several physics papers.
In a symmetrical field between similar electrodes, the polarity has no effect on the breakdown strength. BUTTTTTTT, dissimilar electrodes may have a pronounced polarity effect. I have never seen this effect in a component power supply, but have observed in a large transformer. The electric strength of some materials is tested with an 'impulse' using a specific ramp period. The physics is obvious - the electric strength can be 2x for low dv/dt. So, for some standards, alternating dc polarity is done to simulate an impulse, which is not the core reason for the process in clause 5.2. There may be specific requirements in the C of A by the NCB or NRTL that specify a specific dc polarity due to y-cap values - lower trip current, or inability to detect incorrect values; but it would seem that this would be observed for any polarity. Finally, I have had an SMT auditor that claimed a "DC hi-pot, with any ramp period, will not correctly test both insulation polarities." Yeah, right; and it will not detect planetary alignment nor stress incurred by plate tectonics. More mumbo-jumbo Bravo Sierra. Brian -----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of Jim Hulbert Sent: Tuesday, February 22, 2011 12:23 PM To: EMC-PSTC ([email protected]) Subject: RE: HiPot Testing - DC Polarity To clarify - the "ground" or "earth" lead from the HiPot tester is connected to product chassis. The "hot" lead from the HiPot tester is connected to Line-Neutral inputs on my product's AC input connector. The DC voltage on the "hot" lead from the tester is negative polarity. I am wondering the rationale for this being negative instead of positive. Jim Hulbert From: [email protected] [mailto:[email protected]] On Behalf Of Jim Hulbert Sent: Tuesday, February 22, 2011 1:29 PM To: EMC-PSTC ([email protected]) Subject: HiPot Testing - DC Polarity When performing the Electric Strength (HiPot) test in UL 60590-1 (or EN 60950-1) section 5.2, either AC or DC test voltages may be applied. When applying the DC voltage, what is the rationale for applying voltage that is negative polarity with respect to ground? Regards, Jim Hulbert Pitney Bowes - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
